VARIABLE FREQUENCY DRIVE
VARIABLE FREQUENCY DRIVE(VFD)
VFD is stand for Variable Frequency Drive, It is an electronic gadget, this gadget is to use for control RPM of different kind of electrical motors like single phase or three phase motors also. This gadget is ability to performing the task is to control the required rpm, like reduce or increase the speed (rpm) of the motor.
In other word, adjust increase or decrease the frequency that result is directly affect the (RPM) of the motor.
VDF is only used in AC motors only.
And can be used in small to large motor also
VFD is to perform without effect the torque, impedance and magnetic flux.
Basic concept how to control speed
Speed of the AC motor is inversely proportional to its number of stator poles, and directly proportional to the supply voltage’s (frequency). Therefore speed of the motor either depend on number of stator poles and second method changed the frequency with the help (VFD).
The number of stator poles is fixed to every motor and cannot be changed.
And another concept (VFD) we can changed and varying the frequency with the help of (vfd) that can be effect the (RPM) speed of the motor.
Advantage of vfd
As VFD usage in HVAC applications has increased, fans, pumps, air handlers, and chillers can benefit from speed control. Variable frequency drives provide the following advantages:
- energy savings
- low motor starting current
- reduction of thermal and mechanical stresses on motors and belts during starts
- simple installation
- high power factor
- lower KVA
Comparison of VFD vs Starter Types
Starter Type Starting Current (% of FLA)
Wye-Delta Starter 200-275%
Solid State Soft Starter 200%
Autotransformer Starter 400-500%
Part Winding Starter 400-500%
Across the Line Starter 600-800%
Motor speed (rpm) is dependent upon frequency.
Varying the frequency output of the VFD controls motor speed:
Speed (rpm) = frequency (hertz) x a hundred and twenty / no.of poles
2-pole motor at different frequencies
3600 rev = sixty hertz x a hundred and twenty / 2 = 3600 rev
3000 rev = fifty hertz x a hundred and twenty / 2 = 3000 rev
2400 rev = forty hertz x a hundred and twenty / 2 = 2400 rev